1. Field of the Invention
The present invention generally relates to an apparatus and method for scheduling users in a mobile communication system. More particularly, the present invention relates to an apparatus and method for scheduling users, taking into account inter-cell interference in a multi-cellular mobile communication system.
2. Description of the Related Art
A mobile communication system provides a variety of high-speed multimedia services to users on radio channels. These services have different Quality of Service (QoS) requirements. For instance, a real-time service such as a video call service is tolerant of transmission errors, although the service is sensitive to transmission delays. A service such as a file download service is opposite case in which it is delay-tolerant and error-sensitive. In this context, radio resources can be efficiently used by controlling data rates for different service types, taking into account the congestion of a wireless network. To do so, the mobile communication system adopts scheduling.
Scheduling is a scheme that efficiently utilizes radio resources by selecting a receiving user, a transmission time, and a data rate, upon requests for services from users. A criterion for the selection is fairness. Two popular notions for fairness are proportional fairness and max-min fairness. Proportional fairness is a form of fairness that allocates the same amount of radio resources to Mobile Stations (MSs) irrespective of the MSs channel statuses. For example, almost the same number of time slots are allocated to an MS in good channel status and an MS in poor channel status. The principle of max-min fairness is to allocate radio resources in such a way that the same amount of data is transmitted to MSs rather than the same amount of radio resources are allocated to them. That is, max-min fairness allocates the same data rate to the MSs. Because a wide range of maximum allowed data rates even with a ten-times difference can be supported for MSs, too many time slots may be allocated to an MS with a low data rate, compared to an MS with a high data rate. On the other hand, proportional fairness is not effective in ensuring QoS because it does not support a predetermined or higher data rate for each MS. To avert these problems, a Generalized Proportional Fair (GPF) scheduler has been proposed to achieve a good compromise between proportional fairness and max-min fairness. A major example of the GPF scheduler is a Proportional Fair (PF) scheduler discussed in U.S. Pat. No. 6,449,490 “Transmitter Directed, Code Division Multiple Access System Using Path Diversity to Equitably Maximize Throughput” filed on Sep. 10, 2002.
However, the PF scheduler is designed for a single cell, with no regard to inter-cell interference under a multi-cellular mobile communication environment. In a multi-cellular mobile communication system, an MS at a cell boundary often cannot receive a service due to interference from neighbor cells. Therefore, a fair service is not expected from the PF scheduler. Even if the MS receives the service, the MSs' required QoS is not satisfied because of the neighbor-cell interference. As illustrated in FIGS. 1A and 1B, the neighbor-cell interference decreases a required QoS in the multi-cell mobile communication system. Referring to FIG. 1A, when an MS 104 serviced by a BS 100 (BS A) is located at the boundary of the service area 106 of BS A, a signal from a neighbor BS 102 (BS B) interferes with the MS 104. Due to the interference from BS B, the MS 104 fails to receive a service from BS A or if a service is received, the MS 104 receives the service with a degraded QoS. Referring to FIG. 1B, when an MS 107 serviced by a BS 101 (BS A) is located at the boundary of the service area 110 of BS A, signals from neighbor BSs 103 and 105 (BS B and BS C) interfere with the MS 107. Due to the interference from BS B and BS C, the MS 107 fails to receive a service from BS A or if a service is received, the MS 107 receives the service with a degraded QoS.
Accordingly, there exists a need for an apparatus and method for scheduling MSs, taking into account interference from neighbor cells, while supporting proportional fairness and max-min fairness in a multi-cellular mobile communication system.